<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        body,html{
            padding: 0px;
            margin: 0px;
            height: 100%;
        }
        .left {
            height: 100%;
            width: 300px;
            background-color: lightgray;
            float: left;
        }

        .right {
            height: 100%;
            width: 300px;
            background-color: lightgray;
            float: right;
        }

        .content{
            height: 100%;
            background-color: lightgreen;
            overflow: hidden;
        }
    </style>
</head>

<body>
    <div class="left"></div>
    <div class="right"></div>
    <div class="content"></div>
</body>

</html>